1. Field of the Invention
The present invention relates to a vehicle headlamp, particularly relates to a vehicle headlamp for forming a predetermined light distribution pattern by overlapping light emitted from a plurality of light sources.
2. Related Art
In a background art, as a vehicle headlamp (headlamp), it is general to use a halogen bulb or a discharge bulb as a light source and reflect light emitted from the light source to a front side by using a reflector or a projecting lens. Although a halogen bulb or a discharge bulb is a light source capable of ensuring a sufficient light amount for vehicular use, a problem that power consumption is large is posed.
On the other hand, there is a high tendency of adopting a semiconductor light emitting element such as a light emitting diode as a light source for a vehicle headlamp. A light emitting diode is generally small-sized and power consumption thereof is small and therefore, it is expected to realize to effectively use limited power by being applied to a vehicle mounted with a battery such as an automobile.
Although high luminance formation of a light emitting diode has been promoted, in comparison with a halogen bulb or a discharge bulb, a luminance thereof is not sufficient yet, and a light amount capable of sufficiently ensuring optical recognizability cannot be irradiated to a front side by simply replacing a halogen bulb or a discharge bulb by a light emitting diode. Therefore, currently, it is general to conceive such that a plurality of light source units respectively including light emitting diodes is mounted to a vehicle and a desired light distribution pattern is formed by overlapping light emitted from the light source units.
For example, JP-A-2004-095480 discloses a vehicle headlamp for forming a synthesized light distribution pattern for low beam by combining three pieces of units for forming a cutoff line, five pieces of units for forming a hot zone, and three pieces of units for forming a diverging region. According to the vehicle headlamp, semiconductor light emitting elements are used in all of the units as the light sources, and the vehicle headlamp is constituted to form a light distribution pattern for low beam having a pertinent light amount by overlapping light distribution patterns formed by respectives thereof.
Further, JP-A-2005-141918 discloses a vehicle headlamp for forming a main light distribution by using a projector type light source unit using a discharge bulb, and using an additional light source unit using a semiconductor light emitting element, capable of being switched on and off and capable of being swiveled in a left and right direction and forming a synthesized light distribution pattern by overlapping an auxiliary light distribution on the main light distribution. According to the vehicle headlamp, for example, by switching on the additional light source unit in turning a vehicle and forming the additional light distribution pattern in a direction in accordance with a turning direction, side optical recognizability of a vehicle, particularly, optical recognizability in the turning direction can be promoted.
However, when the synthesized light distribution pattern is intended to provide by combining a plurality of units as in JP-A-2004-095480, power consumption is increased necessarily in accordance with a number of the semiconductor light emitting elements. Therefore, as a realistic vehicle headlamp, it is preferable to construct a constitution having a number of units as small as possible, that is, a number of semiconductor light emitting elements as small as possible.
Further, even when the number of the semiconductor light emitting elements is reduced, it is preferable to construct a constitution capable of forming a light distribution pattern as pertinent as possible in accordance with a situation.